Metal Free is a powerfully effective metal, stain, and scale reducer/eliminator which inhibits the formation of rusty, green, brown, black or cloudy precipitates in spa water. It can also be added to clear up metal coloration already present in your hot tub. Regular use helps prevent scale formation. Most water discoloration problems result from the presence of metallic impurities such as iron (rusty color), copper (green) or other minerals (black, brown, etc). These discolorations may be present in the source water, or can be the result of the acidic action of water with low pH on: spa pipes, metal heater parts, and equipment. Use Metal Free regularly, and these problems are soon gone.